fix: correct PageRank initialization and handle dangling nodes

[mithunbabbira]

Summary

Fixes #14885 - PageRank initializes ranks to 1 instead of 1/n, ignores dangling nodes

Problem

1. PageRank initializes all ranks to 1 instead of 1/n (should be uniform distribution)
2. Dangling nodes (nodes with no outbound links) cause division by zero errors
3. No docstring or tests for the function

Solution

1. Changed rank initialization from 1 to 1/n
2. Added handling for dangling nodes
3. Added comprehensive doctests

Testing

• All doctests pass
• No division by zero errors

Fixes #14885

[algorithms-keeper]

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